Cutting tools

ABSTRACT

The invention provides a cutting tool for incising a helical cut around the internal surface of a hollow member comprising a tool carrier adapted for insertion into the hollow member adjacent the internal surface thereof to be cut; a cutting block carried by the tool carrier and adapted so as to be located, in use, within the hollow member, the block being freely pivotally mounted on the carrier about an axis normal to the axis of relative rotation, in use, of the carrier and the hollow member, and a cutting member secured to the cutting block and extending from the block generally parallel to the axis of pivot thereof upon the carrier, and being arranged such that, in use, as the tool moves (relative to the hollow member) in a helical path around the internal surface, the cutting edge of the cutting member moves (relative to the hollow member) in a direction generally towards the axis of the pivot of the cutting block on the shaft.

BACKGROUND OF THE INVENTION

This invention relates to cutting tools. More particularly the inventionrelates to tools for making a helical incision around the inner surfaceof hollow bodies, such as tubular hollow bodies.

Such tools have been proposed in which the cutting blade is mounted on ashaft arranged to project within the hollow body parallel to the axisthereof the cutting blade projecting outwardly from the shaft so as toimpinge upon the internal surface of the hollow member. Appropriateaxial and radial relative movement between the shaft and the member tobe cut then results in the formation of a helical cut. Usually therelevant movement is caused by rotating the hollow member with thecutting blade engaging the internal surface of the body, and at the sametime axially moving the shaft carrying the cutting blade.

Such a cutting operation is required, for example, in the production ofelectroweld couplings for thermoplastic pipes. In this case a sleeve ofthermoplastic material is provided, in one type of such coupling, with aheating wire inserted in helical fashion within the internal surfacethereof. The insertion of the wire can be achieved by incising a helicalcut or groove around the internal surface of the sleeve, and theninserting the heating wire into the cut or groove so formed. Couplingsof this kind can utilise a sleeve of a very wide range of sizes, fromsay 20 mm internal diameter up to 200 mm internal diameter.

It has been found in practical usage of electroweld couplings of thekind mentioned hereinabove that for couplings intended to connecttogether two pipes, whilst there is need for a relatively close pitchedhelical formation of the heating wire adjacent each end of the couplingso as to achieve satisfactory melting and fusion of the coupling sleeveand pipes during the fusion process, there is no need for the same closepitched spiral across the central portion of the coupling sleeve, andindeed the provision of a close pitched spiral throughout the totallength of the sleeve can be disadvantageous in that greater electricalpower is required for fusion than is necessary on an optimum efficiencybasis, and that an unnecessary length of heating wire is incorporated inthe sleeve.

It has been proposed that the cutting tool should be programmed so as toform a close pitched helical incision adjacent each end of the couplingsleeve, whilst a much wider pitch should be provided over the centralportion of the sleeve such that, for example, the tool traverses thecentral portion in 1 or 1.5 revolutions of the coupling sleeve relativeto the tool.

A difficulty arising from such a proposal however is that the cuttingtool must be capable of cutting at a variable helix angle. This inpractice would require a "backing off" or tapering of the cutting bladefrom its leading to its trailing edge to enable the different helixangles to be cut without the trailing edge of the tool fouling on a sideof the incision made. With the dimensions of the range of pipesconcerned, and the consequent dimensions of the tool and its cuttingblade, adequate backing off to achieve the variation in helix angle isdifficult to achieve and results in a substantially weakened cuttingblade.

It is an object of the present invention to overcome or at leastsubstantially reduce the above mentioned problem.

SUMMARY OF THE INVENTION

According to the invention there is provided a cutting tool for incisinga helical cut around the internal surface of a hollow member comprisinga tool carrier adapted for insertion into the hollow member adjacent theinternal surface thereof to be cut; a cutting block carried by the toolcarrier and adapted so as to be located in use, within the hollowmember, the block being freely pivotally mounted on the carrier about anaxis normal to the axis of relative rotation, in use of the carrier andthe hollow member; and a cutting member secured to the cutting block andextending from the block generally parallel to the axis of pivot thereofupon the carrier, and being arranged such that in use, as the tool moves(relative to the hollow member) in a helical path around the internalsurface, the cutting edge of the cutting member moves (relative to thehollow member) in a direction generally towards the axis of the pivot ofthe cutting block on the shaft.

The tool carrier may comprise a shaft adapted for alignment in use withits longitudinal axis parallel to the axis of relative rotation of thetool and the hollow member. The cutting block may be carried at one endof the shaft and extend generally axially thereof, said block beingfreely pivotally mounted on the end of the shaft about an axis offsetfrom and normal to the axis of the shaft.

The cutting member may be mounted on the cutting block approximatelysuch that in use it intersects the axis of the shaft normally thereto.

The cutting block may be provided with a stop, which may be adjustable,so as to limit its movement about its pivot connection to the shaft.Such limit may be in one or both senses of movement.

By means of the invention a range of helix angles of cutting by thecutting tool can be readily accommodated, in that in use as the shaft iswithdrawn from the rotating hollow member being cut, the cutting blockwill turn on its pivot connection to the shaft such that the cuttingmember is aligned with the desired angle required, such angle beingdetermined by the relative rotational and axial speeds of the hollowmember and tool respectively.

The cutting member may have a cutting blade inclined to the surface ofthe internal wall of the hollow member being cut so as to provide aninclined or angled incision helically around the internal wall. Theangle of inclination may be between 40° and 50°.

In order that the invention may be more readily understood oneembodiment thereof will now be described by way of example withreference to the accompanying drawings in which:

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic isometric view of one end of part of a cuttingtool according to the invention;

FIG. 2 is a side elevation of the tool of FIG. 1;

FIG. 3 is a side elevation of the tool of FIG. 1 showing the cuttingblock in a different angle of position on its pivot pin;

FIG. 4 is an end elevation of the tool of FIG. 1; and

FIG. 5 is a top plan view of the tool of FIG. 1.

DETAILED DESCRIPTION OF THE DRAWINGS

The tool illustrated is intended to provide an incision within the innerwall of a thermoplastic sleeve for an electroweld coupling within whicha heating wire may be located.

Referring to the drawings it will be seen that the cutting toolcomprises a cylindrical steel shaft 1 carrying at one end a cuttingblock 2. The cutting block is pivotably and freely mounted on the shaftby means of a pivot pin 3 which passes through two longitudinallyextending collars 4 of the shaft and through a spur 5 of the cuttingblock. As can be seen, the pivot pin 3 is located on an axis 6 offsetfrom and normal to the longitudinal axis 7 of the shaft.

The cutting block 2 is provided with a rectangular section bore 8 withinwhich is located a cutting member 9 from which protrudes a cutting blade10. The cutting member 9 is held within the block by means of screws 11.(not shown on FIG. 1 for the sake of clarity). As can be seen thecutting member is located so as to pass, when in use, through the axisof the shaft, the cutting member 9 lying generally parallel to the axisof the pivot pin, and the cutting blade 10 passing through a planeincluding the axis of the shaft and parallel to the axis of the pivotpin. As can be seen in comparing FIGS. 2 and 3, the cutting block iscapable of pivotal movement about the pivot pin between a position whereit abuts against the end of the shaft, and a position where it isconsiderably separated from the end of the shaft. A set screw 12 (notshown in FIG. 1 for the sake of clarity) is provided such that theabutting position of the cutting block against the shaft can becontrolled.

As can best be seen in FIGS. 1 and 5 the cutting blade 10 is at an angleof 45° to the general longitudinal direction of the cutting member. Thisensures that the internal surface of the sleeve to be cut is providedwith an inclined incision of an equivalent angle.

In operation the tool is mounted in accordance with normal practice in alathe and is disposed within and at the innermost end of a sleeve (notshown) mounted for rotation about the shaft. The shaft is so alignedthat the cutting edge of the blade cuts into the internal wall of thesleeve. The sleeve is then rotated such that the cutting edge 14 ofblade 10 moves in the direction of the arrow 13 (shown in FIG. 4)relative to the sleeve, whilst at the same time the shaft is withdrawnfrom the sleeve so that the cutting blade 10 incises a close pitchedhelix in the internal wall of the sleeve. At this time the cutting block2 is located as illustrated in FIG. 2. The cutting operation continuesuntil an adequate extent of close pitch helix is formed at that end ofthe sleeve. Whilst rotation of the sleeve continues, the rate ofwithdrawal of the shaft is now increased so that the helix angle of theincised cut is significantly increased. The increase in withdrawal rateof the shaft causes the cutting block to pivot to the position shown inFIG. 3 to enable the cutting blade to follow and incise at the requiredhelix angle. By this means a sharp angled helix is cut across thecentral portion of the sleeve. In practice this can be such as toprovide a spacing between turns of, for example, between 25 and 50% ofthe diameter of the sleeve.

Once the required predetermined central portion of the sleeve has beenpassed the withdrawal rate of the shaft from the rotating sleeve can bereduced so that a second series of helical close pitched incisions canbe made adjacent to the second end of the sleeve. During this operationthe cutting block relocates on the shaft in the position shown in FIG.2.

After the cutting operation by means of the cutting tool according tothe invention a heating wire may be laid in the helical incision formedwithin the sleeve which may then be used in normal manner forelectrofusion coupling purposes.

By means of the invention we have provided a cutting tool capable offorming within hollow members a helical incision of variable pitch anglewithout any need to "back off" the cutting blade, whilst still ensuringsatisfactory clean cutting of the workpiece.

What is claimed is:
 1. A cutting tool for incising a helical cut aroundthe internal surface of a hollow member comprising: tool carrier meansdefining a longitudinal axis for insertion into the hollow memberadjacent the internal surface thereof to be cut; cutting block meanscarried by the tool carrier means, the block means being freelypivotally mounted on the carrier about an axis normal to the axis ofrelative rotation of the carrier means and the hollow member; and acutting member secured to the cutting block means and extending from theblock means generally parallel to the axis of pivot thereof upon thecarrier means, whereby as the tool moves in a helical path around theinternal surface, the cutting edge of the cutting member moves in adirection generally towards the axis of the pivot of the cutting blockmeans on the tool carrier means, whereby in cutting use the cuttingblock means turns on its pivot connection on the tool carrier means suchthat the cutting member is aligned with and cuts at a helical angledetermined by the relative rotational and axial speeds of the hollowmember and tool during cutting.
 2. A cutting tool as claimed in claim 1wherein the tool carrier means comprises a shaft aligned with itslongitudinal axis parallel to the axis of relative rotation of the tooland the hollow member.
 3. A cutting tool as claimed in claim 2 whereinthe cutting block means is carried at one end of the shaft and extendsgenerally axially thereof, said block means being freely pivotallymounted on one end of the shaft about an axis offset from and normal tothe axis of the shaft.
 4. A cutting tool as claimed in claim 3 whereinthe cutting member is mounted on the cutting block means approximatelysuch that in use it intersects the axis of the shaft normally thereto.5. A cutting tool as claimed in claim 2 wherein the cutting block meansis provided with a stop to limit its movement about its pivot connectionto the shaft.
 6. A cutting tool as claimed in claim 5 wherein the stopis adjustable.
 7. A cutting tool as claimed in claim 5 wherein the stopacts to limit movement in one sense only.
 8. A cutting tool as claimedin claim 1 wherein the cutting member has a cutting blade inclined tothe surface of the internal wall of the hollow member being cut so as toprovide an inclined or angled incision helically around the internalwall.
 9. A cutting tool as claimed in claim 8 wherein the cutting bladeis inclined at an angle of inclination of between 40° and 50°.
 10. Acutting tool for incising a helical cut around the internal surface of ahollow member comprising: tool carrier means for insertion into thehollow member adjacent the internal surface thereof to be cut, the toolcarrier means comprising a shaft with its longitudinal axis alignedparallel to the axis of relative rotation of the tool and the hollowmember; cutting block means carried by the tool carrier means andextending generally axially thereof, the block means being freelypivotally mounted on the carrier means about an axis offset from andnormal to the axis of the shaft; and a cutting member secured to thecutting block means and extending from the block means with itslongitudinal axis generally parallel to the axis of pivot thereof uponthe carrier means and approximately intersecting the axis of the shaftnormally thereto, whereby as the tool moves in a helical path around theinternal surface, the cutting edge of the cutting member moves in adirection generally towards the axis of the pivot of the cutting blockmeans on the shaft; whereby in cutting use the cutting block means turnson its pivotal connection on the tool carrier means such that thecutting member is aligned with and cuts at a helical angle determined bythe relative rotational and axial speeds of the hollow member and toolduring cutting.